1. Field of the Invention
The present invention relates to a valve system timing device, including at least a shut-off member, for pressure fluid pipes. More particularly, it relates to a valve system timing device for pressure fluid pipes having the purpose of avoiding, at the opening and at the closing steps, the occurrence in the system of any dangerous water hammers, even though the pressure in the upstream pipe changes considerably, and a pressure gradient occurs in the downstream pipe so as to result in a non-negligible positive or negative difference in height with respect to the shut-off member.
2. Description of the Prior Art
It is well known that a shutting-off member, placed along a water (or other liquid) pipe under pressure, should be operated by a person of particular skill to avoid the occurrence of any overpressure (water hammers) which are extremely dangerous to the whole system (pipes, pumps, valves, etc.). The handling becomes particularly delicate when the initially empty pipe section downstream of the shut-off member is provided with one or more nozzles such as, for example, a sprinkler's line in an irrigation system or, more generally, with conventional air vents.
While it will suffice at the closing step, in order to avoid the "water hammer", to carry out handling of the shut-off member sufficiently slowly, at the opening step it is essential to operate in two well defined steps.
The first step, and by far the most sensitive step, referred to as "pressurization" of the downstream pipe, consists of slowly filling up completely the downstream pipe with liquid, and displacing any residual air contained therein.
Such an operation should be carried out extremely slowly. Thus, as shown by significant studies and operative experience, at the time when the outflow of air from the nozzles ceases, and liquid starts to flow out, due to the sudden and great change in density of the fluid flowing in the pipe, for well known reasons the phenomenon of "water hammer" would occur, if the outflow rate were not sufficiently small.
Therefore the second step, consisting of gradual slow opening of the shut-off member, should take place only after completion of the first step.
Usually, such an "intelligent" handling is manually performed by the operator: at the first step by opening a by-pass device positioned upstream and downstream of the shut-off member, or by opening in a small degree the shut-off member; and the second step by gradually opening the shut-off member completely. There are commercially available shut-off members consisting of two shutters, the first of which is gradually opened, and the second of which may be opened only upon the occurrence of a predetermined downstream back-pressure; but this occurs only when the upstream pressure has quite constant values, and when particular positive or negative slopes or gradients are not present in the downstream position.
Therefore, this known device is not independent of any upstream pressure variations, and for any downstream gradients or slopes. U.S. Pat. No. 2,888,953 discloses a device for timing the operation of the valve system interposed in a liquid utilization circuit between a source of liquid under pressure, and a pressure-liquid receiving line.
The disclosed device includes a chamber of a predetermined volume, a first conduit means between the source and the chamber, and a second conduit means between the source and the line.
Calibrated and preferably sharp-edged calibrated restriction means are interposed in both the first and second conduit means so as to be effective to maintain similar flow characteristics therein, and valve means are operatively associated with the conduit means and operable when open to establish two liquid flows.
Therefore, the flow is reduced for the first time, while it is higher in the second time, when another conduit means is open. This patent recites, therefore, a valve system controlled by a liquid pressure responsive valve actuating piston for ensuring two different rates of feeding of a utilization circuit.
Furthermore, in the device of the U.S. Pat. No. 2,888,953, the main valve opens only after a fixed and constant volume of liquid (U) is located in the downstream pipe. This volume (U) is proportional only to the length of the stroke of the valve actuating piston and to the cross-section of the same piston.
Therefore, this volume U is not automatically variable depending on the characteristic (length, size, slope) of the liquid receiving line. This disclosed device, therefore, does not make possible to avoid or prevent the occurrence in the system of any dangerous water hammers.